Steelmaking process



June 1967 B. B. BRATTON STEYELMAKING PROCESS Filed July 16, 1965INVENTOR Billy B. Broflon United States Patent 3,326,670 STEELMAKINGPROCESS Billy B. Bratton, 314 Broadmore Ave., Pittsburgh, Pa. 15228Filed July 16, 1965, Ser. No. 472,540

- 22 Claims. (Cl. 7528) My present invention relates broadly toprocesses for making steel and more particularly to continuous processesfor making steel directly from any finely divided iron-containingmaterial such as iron ore fines, iron ore concentrates, flue dust, millscale, machine shop turnings and the like with virtually no limitationas to minimum percentages of iron, or combination or proportion ofmaterials except as dictated by the changing economic picture. Myprocess is especially suitable for making steel from iron, oreconcentrates which are obtained from low grade iron ore by grinding theore and separating or concentrating the iron rich fractions, and for therecovery of iron from such waste or by product materials as ore fines,flue dust, mill scale, machine shop turnings, etc. The invention alsorelatesto processes for making various-alloy steels directly from thecorresponding ores.

This application is a continuation-in-part of my copending applicationentitled Steelmaking Process, Ser. No. 252,295, filed Jan. 18, 1963, andnow abandoned.

My process constitutes a radically new approach to making eitherordinary or alloy steels by combining reduction melting and refininginto one continuous operation. My process therefore, replaces both thereduction steps, now conventionally accomplished in the blast furnace,and the refinement steps, presently provided in the open hearth oroxygen furnaces. The thermal and chem= ical energy required for myprocess is obtained for example from hydrocarbon gases, silicon andmanganese. The-simplicity, economy, and other related advantages of myprocess is best illustrated by comparison'with pres ent steelmakingmethods. Briefly, such conventional methods include charging sintered orpelletized forms of iron 'ore, flue dust, mill scale, and the like,together with 3,326,670 Patented June 20, 1967 "ice molten metal. Theblast furnace, therefore is unable to operation, oxygen must be added toremove carbon, sili- 'fs'crap, coke and limestone into a blast furnace.In the blast furnace operation, feed stock must be'abrasion resistant towithstand passage down the furnace shaft. The stock must be no less thanA" in diameter to resist entrainment in the high velocity hot gasesflowing upwardly through the stock. The amount of gangue or slag-formingmaterial present in the stock must be at aminimum because slagrestricts-heat distribution in the-bottom of the furnace.

Under ideal operating conditions, iron is lost both by entrainment inthe exhaust gas and in the slag while the reductant, coke is lost in theform of both soot and carbonmonoxide gas in the exhaust. The solidreductant, coke, is the source of the excess carbon and the sulfur andphosphorus which become-dissolved in the molten metal produced and whichare not removed in the blast furnace. y

The physical arrangement within the furnace is such that the pool ofmolten metal and slag is located below the combustion zone at thetuyeres. Therefore, the formation of a slag blanket on top of the moltenmetal restricts the downward flow of heat; This flow is furtherrestricted as the depth of the molten metal pool and the depth of theslag blanket increases throughout the blast furnace process, so thatcare must be taken to prevent cooling to the point of solidification atthe bottom of the con and manganese by oxidation, while sulfur andprosph-orous are reduced with calcium or magnesium fluxes.

In the older, open hearth furnace the pig iron is similarly refined byoxygen released from rusty scrap, mill scale and ore melting in thefurnace, and in some instances, gaseous oxygen blown into the furnace.

Under ideal operating conditions, metal is lost in these conventionalprocesses by both entrainment in the exhaust gas as iron oxide, and inthe slag as iron oxide. Some of the oxygen gas is trapped within themolten metal during this process which must be removed by some otherprocess, for example vacuum degassing.

The time required for operation of the blast furnace is about 6 to 8hours in addition to the time consumed in the sintering or pelletizingoperation. The very impure pig iron extracted from the blast furnace isthen sent to a holding furnace from which smaller charges are withdrawnfrom time to time to an oxygen furnace to further refine the pig ironinto the desired steel. The oxygen furnace. requires about 1 /2 hoursper charge, and in the conventional steelmaking process of more recentdevelopment, has supplanted the open hearth furnace for refining pigiron into steel. The open hearth requires approxi 'mately 8 'to 9 hoursper charge and is still in use at the present time. In present-dayprocesses, iron ore fines, flue dust, and the like, cannot be chargedinto the blast furnace until they have been sintered or otherwiseagglomerated into inch size particles or larger, which is necessary toprevent the fines from being blown out of the blastfurnace, i.e.entrained in the exhaust gases.

j My process and apparatus eliminate the traditional blast furnace inthat very pure iron or soft steel is produced directly from the ore in aconverter or furnace in one reductionstep, after which the desiredsteeladditive s'can be injected either into the converter or the ladle. Thus,the .usual contamination picked up by the pig iron from the blastfurnace, particularly a carbon content as high as 4 percent, is avoided,in addition to effecting tremendous savings in time, equipment, space,materials, and fuel consumed for blast furnaceand holding furnace operations. The steel made in accordance with the present invention can beessentially carbon-free, if desired, and the deleteriously highpercentage of carbon added by the coke in the blast furnace, isobviated. As is well-known, the carbon content of blast furnace pig ironis lowered only with difficulty even in the case of high carbon steelsemploying at most 2 percent carbon. Pig iron also contains deleteriousamounts of silicon and manganese, which have been unavoidably reducedfrom gangue or slagging materials of the ore by the caroxygen furnace.The oxidizing step is eliminated by the invention, along with thenecessity of employing the open hearth or the holding and oxygenfurnaces, since coke is not employed in the novel process presentedherein. Moreover, the higher operating temperature of my disclosedprocess (3000 F. as opposed to 2450 F. in the blast furnace) causes FeOto oxidize any free Si and Mn which may be present.

The conventional blast furnace, cannot be conveniently or economicallyused in the processing of ores having less than 50% Fe content, inasmuchas the greater quantity of slagging materials from such ores produces acorrespondingly thicker layer of slag or gangue material floating on topof the molten Fe pool at the bottom of the blast furnace. When thethickness of the molten slag layer approaches that resulting from theuse of 50% ores, the thermal barrier formed thereby reduces heattransfer from the hot blast immediately above the slag pool to theextent that the molten pool of pig iron on which the slag pool isfloating, may freeze before it can be poured. In my process, however,ores of any economically feasible Fe content can be employed since meansare provided for heating the molten Fe pool. In most cases thetemperature of the molten pool in the blast furnace is even less thanthe melting point of pure iron, so that the pig iron pool is maintainedin a molten condition by virtue of the Fe-C eutectic. In my process,however, the temperature of the pure Fe pool is always maintained abovethe melting point of pure iron, and no significant quantities of carbonare added.

With my novel ore treatment, and apparatus for handling the same, it ispractical to utilize ore fines, ore concentrate, flue dust, mill scale,and the like, of any degree of fineness, as long as at least 10% of theiron-containing material is below A1 in particle size. As will bepointed out below, maximum efficiency of the novel processes is attainedwith the smallest practical particle size.

In my process, finely divided iron-containing material, usually iron oreconcentrates and proportions of such others listed previously as areeconomically advantageous, all of known chemical composition, areweighed and transferred to a preheat chamber of special design Where thefine materials are heated and partially reduced by exhaust gas from thefurnace. This material then passes through a jet aspirator of specialdesign to withstand high temperatures, for treatment with molten slag.The molten slag binds the iron-containing material into a cohesive,semiplastic solid which is charged into a special furnace which is bothrotatable and tiltable. The furnace charge can include as much as 50%scrap. Oxygen is removed from the iron oxides in the preheat chamber byhydrocarbon gases, and in the furnace by hydrocarbon gases alone or inconjunction with silicon and manganese. Where hydrocarbon gases are usedthe by-products are CO and H gas, and where silicon and manganese areused, the by-products are molten SiO and molten MnO in which case themolten SiO and MnO are subjected to hydrocarbon gases for the removal ofoxygen, after which the free silicon and manganese are ready for reuse.The furnace exhaust gas, containing significant amounts of hydrocarbongases and sensible heat, is piped to the preheat chamber where both arerecovered, and, at the end of each cycle, the molten slag, containingsilicon and manganese where desired, is circulated through a mixer suchas a jet aspirator as an ore treatment, to remove oxygen by exothermicreaction, and to recover sensible heat. In this manner, metallit: oxidesare converted to pure molten metal as the oxygen is converted to CO andH 0 gas and exhausted from the furnace, with a minimum of thermal andchemical energy, material and equipment.

Slag exists in the reduction process as a result of impurities presentin the ores from which metals are extracted. Silica sands comprise themost abundant impurity, followed by clays and other minerals. Slags inwhich silica is the principal mineral will absorb oxygen and thus areconsidered acidic or reducing. Slags of this type are most suitable formy process. The molten slag must be fluid at the jet aspirator and mustmaintain plasticity in the ore and molten slag mixture. Thesecharacteristics are stabilized in the acid slag used in my process bythe addition of manganese and dolomite. One example of an acid slag isas follows:

Percent Si0 48 A1 0 2 FeO 15 MnO 18 CaO+MgO 17 In this example, the SiOand A1 0 are the sand and clay from the ore, the FeO represents theoxide in equilibrium with pure metal and the MnO, CaO and MgO are thefluxes added to stabilize the slag.

If an acidic slag having approximately the aforementioned composition isnot available, as when starting up a new furnace or converter, anartificial slag can be formulated.

Alternatively, an acidic slag can be obtained by melting a correspondingquantity of low-grade iron ore and using the mixture thus obtained asthe molten slag component of the charge. A larger percentage of FeO andan Fe O component would result but these would not affect the desiredslag characteristics. Another alternative would be to obtain slag fromanother furnace of the type used herein, or from an open hearth or anoxygen furnace, if any one of these is within shipping distance.

As stated above, sulfur and phosphorus can enter the process, forexample when flue dust from some other source is being recovered, and insome instances when pyrites and other sulfur or phosphorus bearing oresare used. Sulfur and phosphorus can be prevented from entering the metalby maintaining an oxidizing slag. The slag is rendered oxidizing orbasic by the addition of calcium minerals in the ratio of 1.25 to 1.5parts calcium minerals to 1 part silica.

One example of a basic slag is as follows:

Percent SiO 18 FeO 12 MnO 8 A1 0 3 CaO 43 MgO 8 P 0 8 S-Trace 100 Inthis example, the SiO and A1 0 are the sand and clay from the ore, theFeO represents the oxide in equilibrium with pure metal. The S and P 0are the sulfur and phosphorus, and the MnO, CaO and MgO are the fluxesadded to render the slag basic and to stabilize it.

For succeeding charges, the molten slag will be recycled and itsfluidity and desired melting temperature maintained by a bleed and feedsystem whereby excess molten slag is discarded from the process aftereach charge and additional fluxing agent added to balance the materialspicked up from each charge of iron ore.

In contrast to the limitations to heat transfer known to exist in ablast furnace, my process, through the use of a revolving furnace, isable to achieve direct reducing gas to charge contact throughout theentire melting period and to control the temperature of the molten steelformed without regard to the thickness of a slag layer present in thefurnace.

As the mixture of finely divided iron bearing material and molten slagenters the furnace it will form a level surface due to its semi-plastic,or fluid, nature. Sufficient friction exists between the mass and therefractory lining so that when the furnace is caused to revolve thelevel surface of the mass will incline in the direction of rotation,

O with the angle of inclination increasing until the gravitationalforces acting on the mass equal the frictional resistance between themass and the furnace lining.

A gas lance is inserted into the space above the level of the mass tosupply heat for the reaction and to prevent air from entering thefurnace. Natural gas or methane is used for this purpose and the amountof air or oxygen supplied to the gas is insufi'icient to supportcomplete combustion, so that a reducing atmosphere is maintained. Thegas temperature will approach 3600 F. Reducing gases, such as carbonmonoxide, or hydrogen are directed at the surface of the mass by asecond lance inserted near the first. In this arrangement of my processiron bearing particles composing the surface of the mass are brought upto melting temperature while receiving maximum contact with reducinggases. Molten iron and slag will flow off the inclined surface andcollect at the low point of the converter where they form a stratifiedpool similar to that in a stationary furnace. This exposes the nextlayer to the gas and this sequence is continued until all of the masshas been melted. The exposed area of the furnace lining absorbs heatfrom the burning gases during each revolution. This stored heat isreturned by direct contact to the lowest or coolest level of the moltensteel pool in a continuous flow. The operation of the process is basedon chemical analysis of the iron bearing materials and the molten slag.This analysis provides the temperature and gas requirements for thedesired rate of reduction. Rate of gas flow and furnace rotational speedare thus established. The progress of reduction is checked by monitoringgas flow, furnace temperature, exhaust gas temperature, exhaust gasanalysis and furnace rotational speed and correlating this data withthat known to yield the desired product. The gases and rotational speedare varied as required to maintain the desired correlation. Metal andslag analysis are verified at the end of refining by analysis of actualsamples taken from the furnace.

In another arrangement of my process, acidic or silica slag, is furtheractivated in accordance with one feature of theinvention. In thisarrangement the silica content of the slag markedly predominates and ispartially reduced, together with any MnO present, to obtain a quantityof free silicon (and manganese) after each charge, after which themolten silicon-containing slag is recycled to succeeding charges.Reduction of the silica content is continued to the extent thatsufiicient free silicon, and manganese' if present, is supplied asrequired for exothermic reduction of the iron oxides of the nextsucceeding charge. Excess heat from this reaction being sufiicient tomelt scrap steel amounting to 50% of the furnace charge. In this form ofmy process molten slag is retained for further reduction in the furnace,after the steel is poured off.

The furnace is returned to its operating position and gas lances arereinserted. The reductant gas for this reaction is natural gas(principally CH The surface temperature of the slag reachesapproximately 3400 F. during this reaction. The percentage of silicon(and manganese) reduced from silica (and MnO in forming the thusactivated slag canbe varied to suit the quantity of steel to be producedin the succeeding batch.

In an exemplary arrangement of my novel apparatus, the gases exhaustedfrom the furnace or converter which contain considerable amounts ofuncombusted gases are flowed through a preheater for the iron-containingmaterial whereby a portion of the latter is partially reduced inaddition to advantageously preheating the material for subsequentcomplete reduction steps. The preheater capacity and the volume ofexhaust gases flowed thereto are controlled such that the ore particleswill be suspended or fluidized in accordance with known fluidizationtechniques. Such fluidization facilitates reduction of theiron-containing material through greatly increased gas-solids contact.Where ordinary steels are to be produced, the furnace reductionrequirement is reduced by the amount of reduction achieved in theaforementioned preheat chamber. Where chromium or other alloy componentis to be reduced for alloying with steel, I prefer to employ the freesilicon or activated slag as the molten slag binder for my process. Theslag must be sufii ciently activated to reduce the chromium sincereduction of chromium ores require higher temperatures than normallyobtained with gaseous reductants. The chromium and activated slag mustbe mixed and their exothermic reaction allowed to take place in thefurnace first, because of the higher temperatures required. Theremaining activated slag is then mixed with iron ore and other alloycomponent ores, if used, and put in the furnace with the previouslyreduced chromium and slag.

It will be understood that when the charge is added to the converter,certain steel additives can be charged therewith or alternately theadditives can be placed in the converter before pouring off the steel,or into the ladle thereof.

Through the ability to reduce and to refine iron-containing particles offine particle size and relatively low Fe content, my process can be usedto recover Fe as pure iron or soft steel from the waste products ofother steelmaking or fabricating processes; such as ore fines andscreenings from iron mines, ore fines and screenings from blast furnacestock piles, flue dust from blast furnaces or open hearths or oxygenfurnaces, mill scale from rolling mills, oxide from pickle liquordisposal, and filings or punchings or trimmings from metal fabrication.

These and other objects, features, and advantages of the inventiontogether with method steps and structural details thereof will beelaborated upon during the forth-' coming description of illustrativeforms of the invention, with the description being taken in conjunctionwith the accompanying drawings wherein FIGURE 1 is a schematicrepresentation of the converter or furnace used in the practice of theprocess together with ore, slag, and gas handling equipment associatedtherewith;

FIGURE 2 is a schematic representation ofv the com-. postion and theprogressive partial reduction of typical iron ore particles inthepresenceof hydrogen gas; and- FIGURE 3 is a schematic representation ofthe com position and the progressive partial. reduction of typical ironore particles in the presence of carbon monoxide gas.

In the following description and examples, the material comprising thecharge is iron ore concentrate, the reason being that this is themost-abundant of the above-. mentioned materials and is, therefore, tobe the primary material used. However, the other named materials maylikewise be used separately or together with theprimary material andshould not be considered as less desirable. Iron ore of a particle sizeless than inch is generally considered'to be and is commonly referred toas iron ore fines and will be the primary material being. consideredhere. Steel scrap in the amount of up to. 50% of the total charge can,if desired, be added tothe converter after addition of the molten slagcharge. Because of the use. of the preheater 14 which is described indetail below and in which the ore fines are partially reduced, ore finesof the smallest available particle size are desirable to faciliate thereduction reaction, and thus the conventional sintering or otheragglomerating processes are eliminated. However, as further elaborated.upon, the use of the molten slag binder prevents the fines from beingblown out of the furnace.

Referring now more particularly to the drawings, the iron ore fines andthe like are contained in a storage bin arrangement denoted generally byreference character 10, with the individual bins 12 thereof containingdifferent varieties of ore or of other iron-containing fines which maybe economically available at any given time. The iron ore fines andfluxes are extracted and weighed in a known. manner from theirrespective bins and then conveyed to a preheating chamber 14 by means ofthe continuous conveyor belt 16. In the lower portion of the chamber afrustoconical bafile arrangement 18 is mounted through the spaces ofwhich exhaust converter gases are conducted from a flue stack 20. Theexhaust gases are composed of gaseous reaction products, the excess gassupplied to maintain reaction rate, and the products of heating gascombustion, all of which are noted in greater detail below.

The baffies 18 also serve to direct the powdered ore and the likecontained in the preheater downwardly through a centrally disposedoutlet conduit 22 to a suitable mixer such as a jet aspirator 24. Thevelocity of the exhaust gases through the preheater varies from 40 to 80feet per second, which is sufficient to fluidize most of the particles,and thus to provide intimate contact between the ore particles andexhaust gases for reduction purposes. A variable speed feeder 15transfers the charge from the preheat chamber 14 to the jet aspirator24. Here, the iron-containing fines are treated with molten slag whichis dumped into the runner 26 from the ladle 28 as denoted by dashed line31.

The hot exhaust gases passing, as aforesaid, through the preheater 14reduce at least a portion of the Fe O to FeO thereby minimizing thequantity of gases required for reduction in the converter 30.

The reduction reactions in the preheater are as follows:

The foregoing equations show that the combustibles in the exhaust gasconducted from the preheater 14 are completely oxidized.

The reduction reactions in the preheater 14 are solid state reactionswhere the crystalline structure of the iron oxides is modified withoutmelting. If the sintering temperature of any one of the iron-containingminerals composing the ore fines is reached, the individual particlescan stick together and impede the flow of fines from the preheater 14 tothe jet aspirator 24. The lowest liquidus temperature anticipatedtherefor establishes the maximum allowable temperature within thepreheat chamber. A safe maximum temperature for material in thepreheater 14 is therefore 1700 F., and the temperature is maintained ator slightly below this temperature by by-passing a portion of exhaustgases directly to the dust collector 50 through conduit 51 or byadmitting tempering air into the exhaust stack 20 through inlet conduit53.

As shown in FIGURES 2 and 3 of the drawings the reducing gases in thepreheater 14, which gases include primarily H and CO, remove oxygen fromthe ore particles A, which migrates outward therefrom in the form ofwater vapor and CO respectively. At the same time non-liquid Fe ironmigrate inwardly through gaps in the crystallizing lattices left bydisplacement of oxygen to form increasingly thicker shells E about theparticles, until in the case of H reduction, (FIGURE 2) the pressuredrop across the iron shell increases to about 9 p.s.i. to form a barrierto further escape of water vapor. On the other hand, H is the mostefficient reducing gas until the aforementioned, pressure barrier isreached. H therefore, exhibits higher overall reducing efficiency withsmaller sized ore particles where the shell thickness represents alarger percentage of total size. In the CO reduction, however, thepressure of internal CO builds up and cracks the iron shell (FIGURE 3)and reduction of the particles continues so long as available CO ispresent. As reduction continues the particle divides into zones B, C,and D consisting essentially of iron oxides having correspondingly lessoxygen toward the outer periphery of the particles. The zones B, C, andD typically are comprised of wiistite (FeO less than theoreticaloxygen), magnetite (FeOFe O and hematite (Fe O respectively.

The ore particles discharged from the preheat chamber 14 will be invarious stages of solid state reduction. Each particle will consist ofspherical layers of shells. The outer shell will be soid pure iron whileeach succeeding inner shell will be less reduced. The number of layerswill depend on original ore and the state of reduction, for instance aparticle of hematite would have a center of hematite followed by shellsof magnetite, wiistite and iron. Shell thickness is a function of time,with iron increasing until the entire particle is reduced with the finalstages of reduction Occurring for the most part in the converter 30.

In the furnace 30 heat is added from the hot furnace linings in additionto that added by burning a portion of the natural gas atmosphere. Thisis accomplished by blowing a limited quantity of air through the naturalgas lance 42 described below. The added air is not sufficient forcomplete combustion of the natural gas so that the reducing atmosphereis maintained. The added heat melts the aforementioned iron shellssurrounding the ore particles allowing diffusion inward and outward toproceed very rapidly. Due to the physical structure of the mix thistakes place on the surface layer of particles only and proceeds layer bylayer through the entire mix. Molten metal and slag flows off the tiltedsurface of the mix, which is inclined by the action of furnace rotation,to form layers of molten metal and slag. The molten metal is brought upto the refining temperature by heat from the furnace. A gas flow rate isestablished which is in excess of that required to maintain a steadyreaction rate. The gas must have sufficient velocity to impinge on theoxide surface and entrain gaseous reaction products as they diffusethrough the surface of the particles. This excess gas carries thereaction products away from the surface of the particles and into theexhaust stream to prevent vapor blanketing of the particles, whilemaintaining the gas volume to supply reaction requirements.

When the ore and other fines are treated with the molten slag, the rateof heat transfer from the molten slag to the partially reduced fines,the liquidus temperature of the slag, and the temperature to which thefines are preheated determine how long the mixture -will remain plasticafter the fines and molten slag come into contact in the mixer 24. Heat,of course, must flow from the molten slag across the stagnant layer atthe liquid-solid interface and into the cooler solid particle. Theinitial slag temperature is desirably in the range of 32003400 F. andthe initial or preheated temperature of the fines is between 1600 and1700 F. The equilibrium temperature of the resulting mixture therefore,will be above the liquidus temperature of at least some of the slag andiron ore minerals present so that the charge will not solidify before itcan be dumped into the converter 30. Here the fluidity of the charge isincreased through melting of the remainder of the slag and ore mineralsby heat from the furnace linings, and by additional heat from the gaslance 42 or 44, described below.

From the preheater 14, where the hot exhaust gases partially reduce theore and other fines contained therein, the gases pass upwardly through afrustoconical section 46 of the preheater and then through exhaustconduit 48 to a dust collector 50 which can take the form of a cycloneseparator of known design, or the like. The separated fines areconducted back to the preheater 14 through downcomer 52, while theexhaust gases exit from the dust collector 50 through conduit 54 theother end of which outlets into scrubber tank 56. Any additional finesseparated in the tank 56 are conveyed to a sludge filter as denoted byflow arrow 58. From the scrubber 56 the exhaust gases are conductedthrough conduit 60 to an exhaust fan or blower 62 which discharges tothe exhaust stack 64. Because the hot exhaust gases have been conductedthrough the preheater 14 and thoroughly reacted with iron-containingmaterial therein, little or no combustible gas is exhausted to theatmosphere from the exhaust stack 64. Thus, there is virtually no wasteof the 9 various gases blown intothe converter 30 through lances 42 and44 inasmuch as any uncornbusted or unoxidized portions of the naturalgas, CO, and H gases, together with certain products of partialcombustion thereof serve "as reducing agents which are utilizedsubsequently and completely for partial reduction of iron ore in thepreheater 14. Moreover, a considerable portion of waste heat isrecovered from the exhaust gases.

As shown previously as particle size decreases the amount of surfacearea per unit weight increases, and as more surface area is exposed tocontact with reducing gases the rate of reduction increases andtherefore the process becomes more efiicient. This has a greater effecton reduction by hydrogen as shown in FIGURE 2 than on reduction bycarbon monoxide as shown in FIGURE 3. As ores of this type reach the jetaspirator or other mixing means 24 their .total volume will consist offrom 65 to 50% solid with the remaining 35 to 50% void or filled withair. The function of the jet aspirator 24 is to inject molten slag intothese void spaces to eliminate and exclude air and thus bind the oreparticles into a cohesive, plastic, solid of the same total volume asthe original ore.

The molten slag densifies the particle mixture and prevents the incomingfuel and reducing gases from blowing portions of the ore fines and otheriron-containing dusts out of the converter 30. The molten slag alsoserves to increase substantially the heat transfer characteristics ofthe ore fines, in addition to applying the heat of the molten slag (fromthe preceding charge) directly to the charge, which heat is now wastedin conventional proces ses. As a result of recirculating the slag, as itwere, through the jet aspirator 24, converter 30 and the ladle 28 duringsuccessive charges, the heat imparted to the slag from preceding chargesis conserved. The use of the molten slag and ore mixtures alsoeliminates the relatively large volume of air present in the ore fines(and present also in the sintered or pelletized iron-containingmaterials of conventional processes) which slows or otherwise interfereswith the reduction of iron ore to metallic iron or steel. Further, theheat of the molten slag reduces a further portion of the iron oxides tothe native metal, and also serves as a self-fluxing agent for thecharge.

A primary advantage to the use of a molten slag binder is that iron orefines of very small particle size can be used. In other words, the orefines can be used directly as received at the mill without such furthertreatment as the agglomeration step of conventional steelmakingprocesses. The use of very small particles not only aids the partialreduction thereof in the preheater 14 as discussed above in connectionwith FIGURE 2, but also facilitates the complete reduction thereof inthe converter 30. The mix entering the furnace 30 consists of a solidvolume of ore particles with the voids between and around the individualparticles filled with molten slag. The exposed faces of the mix willcontain the same surface area of ore as the face would have if no moltenslag were presout. The important difference is that without the moltenslag the voids normally existing between the individual particles of theore volume would be filled with air or gas, and, when a reducing gaswould impinge on the ore surface, a differential pressure would beestablished between the gas confined in the ore mass and the gas at thesurface. This would cause the ore particles to become entrained in thereducing gas and carried out of the furnace, and would establish aminimum particle size for that pressure differential established by theminimum gas flo'w for reduction. This is not so when molten slag isused, and therefore, there is no lower limit for ore particle sizes thatcan be used.

Thus, considering as an example, one cubic foot of iron ore fines whichis 60% solid and 40% air voids, it would be necessary to add 0.4 cubicfeet of molten slag to fill the void and about 0.1 cubic feet of excessmolten slag to produce the desired volume characteristics, making atotal of 0.5 cubic feet of molten slag which with the 0.6 cubic foot ofiron ore fines (solid) would yield 1.1 cubic feet of molten mixture.Accordingly, with the average solid and void relation of iron ore finesstated above, it can be determined that the final mixture of iron oreand other fines with molten slag will be from about 45 to 60% by volumeof iron ore fines and 40 to 55% by volume of molten slag to produce amixture which is essentially void-free and air free. Any free moistureand Water of hydration in the fines are, of course, driven off in thepreheat chamber 14.

The jet aspirator 24, in one arrangement of the invention, can take theform of a venturi tube through which the molten slag is flowed underpressure. The outlet conduit 22 of the preheater 14 desirably feeds theore vertically and downwardly into the most constricted portion of theventuri tube and preferably on the upper side thereof. Mixing is doneafter the refined metal and the slag from the preceding charge arepoured out of the converter 30, which is then repositioned to reecivethe discharge from the mixer 24. The slag ladle 28 is then positioned todischarge to the mixer runner 26. Slag flow is started first followed byflow of the ore from the preheat chamber 14. A variable vane-type feeder15 or the like is provided at the chamber outlet 22 to control ore flow,while a gate 27 for controlling slag flow is mounted in the mixer runner26. By proper control of ore and slag discharge rates, a mixer dischargeof absolute volume can be achieved. The furnace 30 pivots, as denoted byreference character 32, upon a suitable support 34 and is rotatable bymeans of its circumferential gear 36 in a known manner.

For charging the fines and molten slag into the converter 30, the jetaspirator 24 is desirably positioned with respect to the converter sothat it can discharge downwardly and directly into the converter, whenthe latter is pivoted such that its upper or open end 38 is movedupwardly from the position shown in FIGURE 1 of the drawings. Infurtherance of this purpose, a rotating exhaust hood 4!) or knownconstruction is employed, which normally connects the open end 38 of theconverter with the lower end of the flue stack 20. After the jetaspirator 24 discharges completely into the converter 30, the latter isreturned to its reduction position, and the exhaust hood 40 is revolvedinto position over the mouth of the converter. At this time the preheatchamber-14 is being refilled for the succeeding charge, and the slagladle is returned to its location at the dump position of the converter.As shown above the chemical and thermal energy used by my process toconvert metal oxides to steel can be provided by hydrocarbon and similaror derivative gases. Examples of such gases are hydrogen and carbonmonoxide which can be obtained from natural gas as well as othersources, and methane which is the principal constituent of natural gas.In my process natural gas is assumed to be the most economical source ofhydrogen and carbon monoxide and which are produced from methane andsteam by catalytic reforming (not shown). Hydrogen and carbon monoxideproduced in this manner have about equal total reduction potential andcan be used in the process in the same proportion as formed for maximumetficiency. As shown in FIGURES 2 and 3 hydrogen is more sensitive toparticle size than carbon monoxide and therefore is used moreeificiently in the early stages of reduction.

With the iron ore mixture, now disposed in the cons verter 30 naturalgas and hydrogen gas lances 42 and 44' are extended through the exhausthood 40 and converter and to a limited extent:

These reactions continue during the natural gas and hydrogen blow untilthe proportionate part of the total reduction to be accomplished withhydrogen has been reached as indicated by gas flow measurements, gastemperature and gas analysis, temperature within the preheat chamber andtemperature within the furnace, as measured by suitably placedinstrumentation (not shown). The lance 44 is then switched to carbonmonoxide, or alternatively is removed and replaced with a carbonmonoxide lance after which the carbon monoxide blow is commenced. Thenatural gas blow is continued at this time but can be at a reduced rate,sufficient to maintain a reducing atmosphere.

During the second blow period with carbon monoxide and natural gas, thefollowing reactions take place:

and to a limited extent:

During both blows pure molten iron and molten slag continue to collectat the bottom of the sloping surface of the metallic oxide. When all ofthe oxide has melted the furnace will contain pure molten iron or softsteel and slag. This will be indicated by its effect on furnace and gastemperatures, exhaust gas volume and chemical analysis as indicated bythe instrumentation mentioned earlier. The function of the natural gaslance 42 is to maintain a reducing atmosphere within the furnace and tosupply any thermal energy that may be required to maintain a' desiredrate of reduction. Both the flow rate through the lance and the ratio ofoxygen to natural gas are controlled to maintain desired furnaceconditions. The temperature of the molten pure iron pool beingformedduring these blows is maintained above 2795 F. by heat transferredfrom the furnace refractory lining as the furnace revolves. This is afunction of furnace gas temperature, refractory temperature and speed offurnace rotation, all of which are monitored and controlled through theentire melting c cle.

After all of the metallic oxides have been melted, samples of metal andslag are taken and analyzed. The quantity of alloys to be added ifdesired are based on this analysis. Alloys can be added either in thefurnace 30, or the ladle 28. The lances 42 and 44 are withdrawn, thehood 40 is moved and the furnace 30 is tilted to discharge steel andslag into separate ladles 28.

A more specific example of this form of the invention follows where abasic slag is utilized and in connection therewith the following typicaliron ore analysis by weight is given:

Percent SiO 10.3 CaO .6 MgO .1 A1 3 .9 Mn .1 S .2 F203 FeO 1.7 Ignitionloss 1.0

Total 100.0

The aforementioined ignition losses represent the proportion of orewhich is lost during handling and reduction thereof. Generally, therewill be free moisture and water of crystallization on the order of 3.3%in addition to the foregoing total as indicated above will be eliminatedduring preheating. Ore of the above analysis, therefore, contains 58.7%by weight of Fe and accordingly 3,405 lbs. of such ore would contain oneton of Fe.

Assuming the ore weighs 210 lbs. per cubic foot and is 60% solid and 40%void (including moisture) it can then be calculated that 16.2 cubic feetof dry ore would be required per ton of Fe, which upon furthercalculation is 9.7 cubic feet of ore solids, if the voids could beeliminated. The molten slag requirement therefor would be 40% of 16.2cubic feet or 6.5 cubic feet plus 1.6 cubic feet (10% excess) or 8.1cubic feet total per ton of Fe. The total mixture therefor would be 17.8cubic feet of ore and molten slag mixture per ton of Fe.

The amount of limestone per ton of Fe needed to react With the SiO ofthe analysis would be 125 pounds or about one cubic foot or 0.7 cubicfoot solid. The dry materials from bins 10, including dry ore andlimestone are weighed onto belt conveyor 16 which transfers them to thepreheat chamber 14 where exhaust gases from the converter 30 enter thechamber 14 by way of bafiles 18 from flue stack 20. These gases preheatand partially re duce this ore. At the end of the preceeding cycle orepasses through chute 22 and feeder 15 into jet aspirator 24 where itmeets and absorbs slag from ladle 28 entering through runner 26 and gate27, to initiate the next oreslag cycle.

Assuming a furnace charge of tons Fe is desired, then according to theexample a total of 1850 cubic feet of molten slag, ore, and limestonemixture would be charged into the converter 30, which has beenpositioned to receive the charge. The furnace is then revolved intooperating position, the hood 40 is moved into place and the gas lances42 and 44 are inserted into the converter 30, the converter is startedto rotating, and the blow of hydrogen and natural gas is begun.

The converter 30 in this example is constructed such that its speed ofrotation can be varied from 0-30 r.p.m. The natural gas lance 42 is usedto supply the heat energy necessary to sustain the endothermic reductionreaction and to maintain a reducing atmosphere in the furnace. Theseobjectives are accomplished by burning the natural gas with a deficientoxygen supply. Either oxygen or oxygen-enriched air is supplied throughthe natural gas lance 42 for this purpose. The lance 42 is positioned tosupply heat to this converter lining and to the area above the surfaceof the charge. The converter 30 is rotated at a speed between less thanone and four revolutions per minute while the mix is beginning to melt.After about half of the charge has melted, the carbon monoxide lance 44is used to supply the reductant, while the natural gasoxygen blow fromlance 42 is continued until the con verter charge is completely melted.The converter 30 is rotated during this time at a speed such that thelining temperature is above the minimum temperature to transfersufficient heat to the molten Fe pool to keep the latter from freezing,and below the maximum permissible operating temperature of the lining.These maximum and minimum temperatures will vary with the thickness andtype of furnace linings used, as known to those skilled in the art. TheCO or H lance 44 is positioned so that CO gas will sweep the surface ofthe charge as the converter is rotated, while being heated by thenatural gas from the lance 42.

After melting is complete and samples of metal and slag have been takenand analyzed, the lances 42 and 44 are withdrawn, the hood 40 isrevolved and the furnace 30 is tilted to discharge metal and slag intoseparate ladles 28.

13 Gas requirements as outlined in this example I s.c.f 2500 s.c.f.natural gas 100 tons 250,000 5000 s.c.f. carbon monoxide 100 tons500,000

10,000 s.c.f. hydrogenx tons 1,000, 000 The maximum blowing rates forall gases in this example are 25,000 s.c.f. per minute at 40 pounds persquare inch..

Therefore, the tap to tap time required to convert metallic oxides to100 tons of steel will be as follows:

, Minutes Charging Hydrogen lancing 1,000,000/25,000 g Change lances 10Carbon monoxide lancing 500,000/ 25,000 20 Total 1 120 1 Or 2 hours. v

This time compares favorably with conventional processes where the blastfurnace-open hearth combination could require as much as 16 hours, andthe blast furnace-oxygen furnace as much as 9 hours, for the sameproduction.

Moreover, heat requirements in this example are less than 7,000,000B.t.u. per ton of steel as compared to over 12,000,000 B.t.u. per ton ofsteel by the conventional blast furnaceopen hearth combination,therefore; fuel requirements are less than that of any process known atthis time. W

Since the major proportion of the molten slag issuing from the converter30 is recycled and its sensible heat retained in the process, and sincemost of the exhaust gas heat is recovered in the preheater 14, it willbe evident then, that most of the heat carried out of the process is inthe molten iron. Therefore, the advantages and benefits resulting fromthe aforedescribed process will-be immediately apparent to. thoseskilled in the steelmaking art.

In another form of steelmaking process, in accordance with theinvention, free or metallic silicon (together with metallic manganese ifthe oxide'thereof is present in the molten slag) is generated in themolten slag carrier after the molten iron is poured from the converter30. In this, arrangement of the-invention,- an acidic slag is employed.

having a composition of about SiO A combination of carbon monoxide andhydrogen gases,

which may be reformed from natural gas, is blown against the remainingslag through .the lance 44. At the same time, a reducing atmosphere ismaintainedwithin the converter 30 by blowing natural gas through the.otherlance 42. The CO and H together with a quantity of air ofcombustion supply the necessary. heat required to raise the temperatureof the slag to about 3300 FL, while the natural gas serves as. reducingagent to reduce the silicon dioxide to metallic silicon. 4

During the silicon regenerating cycle,- the followingre- Similarly,where a MnOslagging component is present;

The free silicon and manganese content of -the slag-can be increased sothat final reduction and refinement of the ore to pure iron is achievedby. exothermic reaction with the slag instead of with gasesLThis excessheat'ofthisr'e can be used to melt scrap added with the action thuscharge.

- Completion of the foregoing reaction'is indicatied. when theproportions of natural gas in the exhaust; gases from It is known thatat temperatures below'about 2822 F.

oxygen possesses a greater afiinity for metallic silicon than forcarbon. However, at temperatures above this point, oxygen exhibits agreater affinity for carbon. This is proved in steelmaking practice bythe obsolescent Bessemer process. In the latter process, the hot metalusually contains more carbon than silicon, but when the blowing starts,since the Bessemer process is at temperatures below 2822 F., silicon iscompletely oxidized before the oxidation of carbon commences.

In this form of the invention, the aforementioned change in oxygenafiinities as temperature rises is em ployed to establish a siliconreduction cycle where the greater activity of silicon is employed toreduce iron ore in accordance with the following equations:

The silicon metal, manganese metal, residual free iron, and slaggingmaterial, all of which may be termed active silicon slag, are theninjected into the succeeding charge of ore'fines and the like in the jetaspirator 24. The ladle containing the active silicon slag is dumpedinto runner 26 of the mixer while the temperature of the active siliconslag is still above 3000" F. This temperature is high enough, of course,to commence an immediate reaction with the ore fines delivered to thejet aspirator 24 from the preheater 14. Preheating and partial reductionof the ore fines, of course, further stimulates the last-mentionedreaction. This mixture of active silicon slag and ore fines falls intothe converter 30 when the latter is tilted upwardly and the aforesaidreaction between the ore fines and the active silicon slag is completedin the converter.

Inthe latter-described process, it will be apparent that the regeneratedsilicon metal is the intermediate in the and silicon metal. For tons ofiron ore having theaforestated typical analysis 13- tons of free siliconwill be required.

Where the iron-containing fines initially contain moresulfur orphosphorus than the steel specifications allow, these impurities can bereduced to acceptable values in the steel ladle 28 by the addition ofsoda ash, burnt lime, calcium cyanamide or calcium carbide, which reactwith these impurities. The aforementioned S and P can be in-- troduced'with certain varieties of iron ore, or with flue dust from the blastfurnace or open hearth if used.

The active silicon slag when added to the ore and the like in the'jetaspirator 24 is absorbed into the voids in the ore as describedhereinbefore.

In still another arrangement of my process, a chromesteel orchrome-nickel stainless steel can be produced directly from thecorresponding ores with a modified form of the active silicon slag cycledescribed above. The raw materials for this process are-chrome-ore, ironore, nickel oxide (for Cr-Ni stainless steel) and natural'gas. Dualpreheaters and mixers, corresponding to the preheater 14 and the mixer24, are required because the chrome orev must be reduced at a highertemperature and thus'main tained separately of the iron and nickel oresduring initial stages of the-process.v In the first step of thisprocess, part of a quantity active silicon slag is mixed with a chargeof chrome ore and put into the converter 30, which is rotated. Thereaction of chrome ore-with the free silicon is similar to thatmentioned previously in connection with the'iron-sllicon reaction and isas follows:'

The reaction set forth above commences immediately as Additional heat,if required is supplied by burning a portion of natural gas at the lance42.

After the above reaction is substantially completed, the remainder ofthe active silicon slag is mixed with iron ore (if a chrome-steel alloyis desired) or with combined iron ore and nickel oxide fines (for achrome-nickel-steel alloy) in the other mixer and dumped into theconverter 30 which is rotated to mix the latter charge thoroughly withthe partially reduced chrome ore-molten slag charge therein. Thefollowing exothermic reactions commence immediately upon mixing due tothe molten condition of the active silicon slag and preheating of theore fines:

After completion of the aforementioned reactions, the chrome-nickelstainless steel is poured off into a ladle 28 therefor. Regeneration ofthe silicon slag is accomplished as in the aforedescribed active siliconslag cycle until an amount of free silicon slightly in excess of thatrequired for the reduction of all three ores is recovered from the:silica component of the slag.

The exhaust gases from the converter 30 in this process :are divided bysuitable ductwork (not shown) and conducted to the aforementionedpreheaters where the chrome ore is preheated separately from the ironand nickel ores. To produce the aforementioned chrome-steel alloy, thelast-described process is followed, save that the NiO is omitted.

From the foregoing, it will be apparent that novel and efficientsteelmaking processes have been disclosed herein. The iron content ofore fines and the like is directly reduced into pure iron or steel towhich the desired additive can be added, or alternatively, alloy steelcan be directly reduced with silicon from the corresponding ores. Theillustrative and descriptive material employed herein is presented forpurposes of exemplifying the invention and not in limitation thereof.Therefore, nu- :merous modifications of the invention will occur tothose skilled in the art without departing from the spirit and scope ofthe invention. Moreover, it is to be understood.

that certain features of the invention can be employed without acorresponding usage of other features thereof.

I claim:

1. A process for making steel from finely divided iron- :containingmaterial, said process comprising the steps of completely mixing aquantity of said material into a suspension thereof in molten slag,charging said material and said molten slag suspension into a furnace,blowing com bustible and reducing gases into said furnace, blowing alimited amount of oxygen into said furnace for partial combustion of thecombustible gas to melt completely :said material and to maintain areducing atmosphere, and discharging molten slag and metal separatelyfrom the furnace.

2. The process of claim 1 wherein said finely divided iron-containingmaterial is at least one of the group consisting of iron ore fines, orescreenings, pickle oxide, iron ore concentrates, flue dust, mill scale,shavings, filings, punchings, and turnings.

3. The process of claim 1 wherein the iron-containing material and slagmixture comprises about 45 to 60% by volume of iron ore fines and 40% to55% by volume of molten slag.

4. A process for making steel from finely divided ironcontainingmaterial, said process comprising the steps of mixing a quantity of saidmaterial into a suspension thereof in molten slag, charging the materialand molten slag mixture into a tiltable rotatable converter, blowingnatural gas with insufiicient oxygen for combustion thereof and hydrogenand carbon monoxide gases into the converter to melt and to reducecompletely said material, and discharging the molten slag and metalseparately from the converter.

5. The process of claim 4 wherein the natural gas with insufficientoxygen and hydrogen gas are blown together into the converter until theexhaust gases from the converter indicate a significant increase inhydrogen gas content and thereafter carbon monoxide gas is blown intothe converter.

6. The process of claim 5 wherein said carbon monoxide gas is blown intothe converter until the exhaust gases from the converter indicate asignificant increase in carbon monoxide gas content.

7. The process of claim 5 wherein natural gas is blown into saidconverter with said carbon monoxide to maintain a reducing atmospheretherein.

8. The process of claim 4 wherein the gases are blown each through alance into the converter at the rate of about 25,000 cubic feet perminute at a pressure of about 40 p.s.i.

9. A process for making steel from finely divided ironcontainingmaterial, said process comprising the steps of completely mixing aquantity of said material into a suspension thereof in molten slag,charging said material and molten slag mixture into a furnace, blowingcombustible and reducing gases into said furnace, blowing a limitedamount of oxygen into said furnace for partial combustion of thecombustible gas to melt said material and to maintain a reducingatmosphere, conducting hot exhaust gases from said furnace to asucceeding quantity of said iron-containing material to preheat andreduce partially said last-mentioned iron-containing material, anddischarging molten slag and metal separately from the converter.

10. A process for making steel from finely divided iron-containingmaterial, said process comprising the steps of completely mixing aquantity of said material into a suspension thereof in molten slag,charging said material and slag into a furnace, blowing combustible andreducing gases into said furnace, blowing a limited amount of oxygeninto said furnace for partial combustion of the combustible gas to meltsaid material and to maintain a reducing atmosphere, flowing exhaustgases from said furnace through a succeeding quantity of said materialcontained in a preheat chamber at a velocity sufiicient to fluidize saidlast-mentioned material for the preheating and partial reductionthereof, and discharging molten slag andmetal separately from theconverter.

11. A process for making steel from finely divided iron-containingmaterial, said process comprising the steps of completely mixing aquantity of said material into a suspension thereof in molten slag,charging the mixture into a tiltable rotatable converter, blowingnatural gas with insufficient oxygen for combustion thereof and hydrogenand carbon monoxide gases into the converter to melt and to reducecompletely said material, said natural gas and oxygen being directedagainst the converter lining, and said hydrogen and carbon monoxidegases being directed onto the surface of said mixture while rotating theconverter, and discharging the molten metal and slag separately from theconverter.

12. A process for making steel directly from finely dividediron-containing material, said process comprising the steps of initiallymixing a quantity of said material with molten slag to drive off themoisture from said material, said sla-g being sufficient in quantity atleast to fill entirely the voids among the particles in saidiron-containing material and being not greater in quantity than of thevoid volume of said material, placing the mixture into a furnace,blowing into said furnace combustible and reducing gases to melt andreduce completely said material, and discharging the molten metal andslag separately from said furnace.

13. A process for making steel from finely divided iron-containingmaterial, said process comprising the steps of completely mixing aquantity of said material into a suspension thereof in molten slag,charging said material and slag into a furnace, blowing combustible andreducing gases into said furnace, blowing a limited amount of oxygeninto said furnace for partial combustion of the combustible gas to meltsaid material and to maintain a reducing atmosphere, discharging moltenslag and metal separately from the converter, and recirculating at leasta portion of said discharged slag while molten directly to a succeedingquantity of said iron-containing material.

14. A process for making steel from finely divided iron-containingmaterial, said process comprising the steps of completely mixing aquantity of said material into a suspension thereof in molten slag,charging said material and slag into a furnace, blowing combustible andreducing gases into said furnace, blowing a limited amount of oxygeninto said furnace for partial combustion of the com bustible gas to meltsaid material and to maintain a reducing atmosphere, conducting exhaustgases from said furnace to a succeeding quantity of said iron-containingmaterial to preheat and reduce partially said last-mentioned material,discharging molten slag and metal separately from the converter, andrecirculating at least a portion of said discharging slag while moltendirectly to said succeeding quantity of the iron-containing material.

15. A process for making steel directly from finely dividediron-containing material, said process comprising the steps ofcompletely mixing a quantity of said material with a quantity of moltenfree-silicon-containing slag sufficient at least to fill completely thevoids in said material, charging said mixture into a furnace, heatingsaid mixture suificiently to react said free silicon with said materialto reduce the same, discharging molten iron from said furnace, blowingthe mixture remaining in said furnace with natural gas to regenerate thereacted silicon, discharging molten slag containing free silicon fromsaid furnace, and re-circulating said silicon and at least a portion ofsaid slag to a succeeding charge of said material.

16. A process for making steel directly from finely dividediron-containing material comprising the steps of completely mixing saidmaterial with a quantity of molten free-silicon-containing slagsufiicient at least to fill completely the voids in said material,charging said mixture into a furnace, heating said mixture sufiicientlyto react said silicon with said material, discharging molten iron fromsaid furnace, blowing the mixture in said furnace with natural gas toregenerate the reacted silicon, conveying the hot exhaust gases fromsaid furnace to a succeeding charge of said material to preheat and toreduce partially said material, discharging molten slag containing freesilicon from said furnace, and re-circulating said silicon and at leasta portion of said slag to a succeeding charge of said material.

17. A process for making steel directly from finely dividediron-containing material, said process comprising the steps of initiallymixing said iron-containing material with a quantity of molten slagsufficient at least to fill entirely the voids in said iron-containingmaterials, placing the iron-containing material and molten slag mixtureinto a furnace, blowing the mixture in said furnace with combustible andreducing gases to melt completely said material and to reduce the same,the combustible gas being blown with insuflicient oxygen to supportcomplete combustion thereof whereby a reducing atmosphere is maintainedin said furnace, conveying the hot exhaust gases from said furnace to asucceeding charge of said iron-containing material to preheat and toreduce partially said last-mentioned material, conducting said exhaustgases thence to a dust collector, discharging molten iron and slagseparately from said furnace, and combining the dust output of saidcollector with said succeeding charge of material to preheat said dustoutput.

18. In a process for making alloy steel directly from finely dividedmaterials containing respectively the alloy components of said steel,said process including the steps of mixing a quantity of finely dividedmaterial containing at least one of said components with a quantity ofmolten free-siIicon-containing slag suflicient at least to fill thevoids of said material, placing said mixture into a furnace, blowing themixture in said furnace with natural gas to increase the temperature ofsaid mixture and to react the alloy component containing materialthereof with said silicon to reduce the first-mentioned quantity ofmaterial, mixing a quantity of the remainder of said alloy componentcontaining material with a'quantity of free silicon-containing moltenslag sufficient at least to fill the voids of said last-mentionedquantity of material, placing said last-mentioned mixture in saidfurnace for reduction thereof, discharging molten alloy steel from saidfurnace, blowing the slag remaining in said furnace with natural gas toregenerate the reacted silicon, discharging the molten slag containingfree silicon separately from said furnace, and re-circulating saidmetallic silicon and at least a portion of said molten slag tosucceeding quantities of said materials.

19. A process for making steel directly from finely dividediron-containing material, said process comprising the steps ofcompletely mixing a quantity of said material With a quantity of moltenfree-silicon and manganese-containing slag sufficient at least to fillcompletely the voids in said material, charging said mixture into afurnace, heating said mixture sufficiently to react said silicon andsaid manganese with said material, discharging molten iron from saidfurnace, blowing the mixture remaining in said furnace with natural gasto regenerate the reacted silicon and manganese, discharging molten slagcontaining free silicon and free manganese from said furnace, andre-circulating said silicon and manganese and at least a portion of saidslag to a succeeding quantity of said material.

20. In a process for making chrome-steel alloy directly from thecorresponding ores thereof, said process including the steps of mixing aquantity of chrome ore with a quantity of molten free-silicon-containingslag sufficient at least to fill completely the voids in said chromeore, placing said chrome ore and slag mixture in a furnace, blowing saidmixture with suflicient natural gas and oxygen to raise said mixture toa temperature at which said chrome ore and said silicon will react,mixing a quantity of iron ore and with an additional quantity of saidfree-silicon'containing slag sufficient at least to fill completely thevoids in said iron ore, adding said iron ore and slag mixture to thechrome ore and slag mixture in said furnace after said chrome ore andsilicon reaction has been substantially completed, mixing together saidfirstand said second-mentioned mixtures to react said iron ore andsilicon and to mix thoroughly the resultant molten chromium and ironmetals, discharging said chrome-steel alloy from said furnace, andblowing the remaining slag in said furnace with natural gas and oxygento reduce residual amounts of chrome and iron material in said remainingslag and to regenerate said silicon.

21. The process of claim 20 characterized in that a nickel-chrome-steelalloy is produced by adding a quantity of nickel ore with said quantityof iron ore.

22. The process of claim 20 characterized in that portions of theexhaust gases from said furnace are conducted to succeeding quantitiesof said chrome ore and said iron ore respectively to preheat and toreduce partially the same.

References Cited UNITED STATES PATENTS 55,710 6/1866 Reese 7540 108,23510/1870 Bird 75-30 350,574 10/1886 Wainwright 75-40 604,580 5/1898Gesner 75-54 920,391 5/1909 Reid 7540 1,081,921 12/1913 Baggaley 7525(Other references on following page) 1 9 UNITED STATES PATENTS Boggs7525 Lund 754'0 Bradley 75-4-0 Lewis 7546 Le Clarick 7525 X Eulensteinet a1. 7540 Pitterer 7524 Gilliland 754'0 Rummel 7540 Johnson 7540Moussoulos 7540 X Rummel 7540 Pfeiffer et a1 7526 DAVID L. RECK, PrimaryExaminer.

H. W. TARRING, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,326,670 June 20 1967 Billy B Bratton It is hereby certified that errorappears in the above numbered patent requiring correction and that thesaid Letters Patent should read as corrected below.

Column 7 line 45 for "1700 F. read 1700 F. column 10 lines 12 and 13 for"prosphorous" read phosphorus line 20, for "reecive" read receive column12 line 50 for "this" read the column 13 line 5 for "10" read 100 column15 line 15 for "2Si Fe" read 2Si-- 3Fe Signed and sealed this 25th dayof June 1968 (SEAL) Attest:

Edward M. Fletcher, Jr. EDWARD J. BRENNER Attesting Officer Commissionerof Patents

1. A PROCESS FOR MAKING STEEL FROM FINELY DIVIDED IRONCONTAININGMATERIAL, SAID PROCESS COMPRISING THE STEPS OF COMPLETELY MIXING AQUANTITY OF SAID MATERIAL INTO A SUSPENSION THEREOF IN MOLTEN SLAG,CHARGING SAID MATERIAL AND SAID MOLTEN SLAG SUSPENSION INTO A FURNACE,BLOWING COMBUSTIBLE AND REDUCING GASES INTO SAID FURNACES, BLOWING A